A float operated, top fill, recovery unit floats in a body of contaminated groundwater to recover a layer of liquid hydrocarbons residing on top of the groundwater. The recovery unit has an upper end fitted with a discharge check valve assembly and a lower end that is closed, the discharge valve assembly...http://www.google.ca/patents/US5495890?utm_source=gb-gplus-sharePatent US5495890 - Float operated pneumatic pump
